Virtual machine systems in which virtual machines (hereinafter sometimes referred to as “VMs”) are caused to operate on physical machines have been used. A technology called VM dynamic migration (hereinafter referred to as “live migration”) is used in such a virtual machine system. In the live migration, the physical machine on which the virtual machine operates is migrated to another physical machine without barely stopping a service provided by the VM.
However, the virtual machine system in the related art described has the problem in that, when Internet Group Management Protocol (IGMP) is applied, the physical machine cannot possibly receive a multicast packet for a certain time after the live migration is executed.
Such a problem is described with reference to FIG. 10. In an example illustrated in FIG. 10, a router 92 and servers 93A and 93B, which are physical machines, are connected to a physical switch 91. A VM 94A, which is a virtual machine, operates on the server 93A. It is assumed that the IGMP is applied to the virtual machine system in FIG. 10. Specifically, the router 92 periodically transmits an IGMP query message to the servers 93A and 93B through the physical switch 91. The servers 93A and 93B transmit an IGMP Host Membership Report message in response to the IGMP query message. If the IGMP Host Membership Report message is a JOIN message, which indicates a delivery request, the physical switch 91 transmits a multicast packet to the server 93A or 93B from which the JOIN message is transmitted.
In the virtual machine system illustrated in FIG. 10, the server 93A transmits a JOIN message but the server 93B does not transmit a JOIN message. In other words, the server 93A receives a multicast packet but the server 93B does not receive a multicast packet. The live migration in which the physical machine on which the VM 94A operates is migrated from the server 93A to the server 93B is executed in such a state. In the above case, the VM 94A cannot receive a multicast message for a certain time after the live migration is completed. This is because the server 93B to which the VM 94A is migrated cannot receive a multicast message during a time after the server 93B receives an IGMP query message from the router 92 before the server 93B transmits a JOIN message in response to the IGMP query message.
The time interval when the IGMP query message is transmitted by the router 92 is generally, 60 seconds or 125 seconds. Accordingly, the VM 94A cannot receive a multicast message, for example, for 60 seconds or 125 seconds after the live migration is completed in the above case.
A technology in which a virtual switch included in a physical switch transmits a pseudo IGMP query message is also proposed in recent years in order to allow a multicast packet to be received after the live migration is completed. However, such a technology cannot be applied to a system that bypasses the virtual switch. For example, such a technology cannot be applied to a system that executes the live migration by direct input-output (I/O). It is difficult to apply such a technology also when the virtual switch is included in a network interface card (NIC) held in the physical machine.